Funds are requested to purchase a ThermoFinnigan LTQ Orbitrap mass spectrometer that will be housed in the Wistar Institute Proteomics Core Facility. This instrument will provide critically needed increased capacity to identify proteins and posttranslational modifications with high confidence in complex samples. A major user group of 8 investigators will utilize 75% of instrument time and 8 minor users will account for an additional 21% of instrument use. Most investigators in both the major and minor user groups have multiple NIH funded research projects that will utilize this instrument. Hence, a linear ion trap mass spectrometer that is fully available to the major user group is critically needed and will greatly advance NIH funded research at the Wistar Institute. The purchase of an LTQ Orbitrap mass spectrometer is strongly preferred rather than a stand- alone LTQ instrument because the LTQ Orbitrap will also provide high resolution and high accuracy measurements of precursor and fragment ion masses. This will greatly enhance the identification of low abundance components in complex mixtures with improved confidence, and it should also improve the confidence of identifications of posttranslational modifications. Even with the addition of the requested LTQ Orbitrap, conservative projections of anticipated workload for 2007 indicate that both this instrument and an existing LTQ will need to be operated near full capacity, 24 hours per day, 7 days a week to keep up with demand. The requested instrument will be incorporated into a Proteomics Core Facility that has provided LC- MS/MS analysis services for the past 6 years to many academic investigators. In 2005, a total of 30 different laboratories used these services and similar numbers of users are anticipated for the future. The Wistar Institute is committed to housing, maintaining and staffing the requested mass spectrometer for its useful lifetime as verified by an accompanying letter from the Institute President and CEO. [unreadable] [unreadable] [unreadable]